[HLSL] Implement output parameter (#101083)

HLSL output parameters are denoted with the `inout` and `out` keywords
in the function declaration. When an argument to an output parameter is
constructed a temporary value is constructed for the argument.

For `inout` pamameters the argument is initialized via copy-initialization
from the argument lvalue expression to the parameter type. For `out`
parameters the argument is not initialized before the call.

In both cases on return of the function the temporary value is written
back to the argument lvalue expression through an implicit assignment
binary operator with casting as required.

This change introduces a new HLSLOutArgExpr ast node which represents
the output argument behavior. The OutArgExpr has three defined children:
- An OpaqueValueExpr of the argument lvalue expression.
- An OpaqueValueExpr of the copy-initialized parameter.
- A BinaryOpExpr assigning the first with the value of the second.

Fixes #87526

---------

Co-authored-by: Damyan Pepper <[email protected]>
Co-authored-by: John McCall <[email protected]>

Author: 3 people

clang/include/clang/AST/ASTContext.h

@@ -1381,6 +1381,14 @@ class ASTContext : public RefCountedBase<ASTContext> {
   /// in the return type and parameter types.
   bool hasSameFunctionTypeIgnoringPtrSizes(QualType T, QualType U);
 
+  /// Get or construct a function type that is equivalent to the input type
+  /// except that the parameter ABI annotations are stripped.
+  QualType getFunctionTypeWithoutParamABIs(QualType T) const;
+
+  /// Determine if two function types are the same, ignoring parameter ABI
+  /// annotations.
+  bool hasSameFunctionTypeIgnoringParamABI(QualType T, QualType U) const;
+
   /// Return the uniqued reference to the type for a complex
   /// number with the specified element type.
   QualType getComplexType(QualType T) const;

clang/include/clang/AST/Attr.h

@@ -224,20 +224,7 @@ class ParameterABIAttr : public InheritableParamAttr {
                              InheritEvenIfAlreadyPresent) {}
 
 public:
-  ParameterABI getABI() const {
-    switch (getKind()) {
-    case attr::SwiftContext:
-      return ParameterABI::SwiftContext;
-    case attr::SwiftAsyncContext:
-      return ParameterABI::SwiftAsyncContext;
-    case attr::SwiftErrorResult:
-      return ParameterABI::SwiftErrorResult;
-    case attr::SwiftIndirectResult:
-      return ParameterABI::SwiftIndirectResult;
-    default:
-      llvm_unreachable("bad parameter ABI attribute kind");
-    }
-  }
+  ParameterABI getABI() const;
 
   static bool classof(const Attr *A) {
     return A->getKind() >= attr::FirstParameterABIAttr &&
@@ -379,6 +366,29 @@ inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
   DB.AddTaggedVal(reinterpret_cast<uint64_t>(At), DiagnosticsEngine::ak_attr);
   return DB;
 }
+
+inline ParameterABI ParameterABIAttr::getABI() const {
+  switch (getKind()) {
+  case attr::SwiftContext:
+    return ParameterABI::SwiftContext;
+  case attr::SwiftAsyncContext:
+    return ParameterABI::SwiftAsyncContext;
+  case attr::SwiftErrorResult:
+    return ParameterABI::SwiftErrorResult;
+  case attr::SwiftIndirectResult:
+    return ParameterABI::SwiftIndirectResult;
+  case attr::HLSLParamModifier: {
+    const auto *A = cast<HLSLParamModifierAttr>(this);
+    if (A->isOut())
+      return ParameterABI::HLSLOut;
+    if (A->isInOut())
+      return ParameterABI::HLSLInOut;
+    return ParameterABI::Ordinary;
+  }
+  default:
+    llvm_unreachable("bad parameter ABI attribute kind");
+  }
+}
 }  // end namespace clang
 
 #endif

clang/include/clang/AST/Expr.h

@@ -7071,6 +7071,103 @@ class ArraySectionExpr : public Expr {
   void setRBracketLoc(SourceLocation L) { RBracketLoc = L; }
 };
 
+/// This class represents temporary values used to represent inout and out
+/// arguments in HLSL. From the callee perspective these parameters are more or
+/// less __restrict__ T&. They are guaranteed to not alias any memory. inout
+/// parameters are initialized by the caller, and out parameters are references
+/// to uninitialized memory.
+///
+/// In the caller, the argument expression creates a temporary in local memory
+/// and the address of the temporary is passed into the callee. There may be
+/// implicit conversion sequences to initialize the temporary, and on expiration
+/// of the temporary an inverse conversion sequence is applied as a write-back
+/// conversion to the source l-value.
+///
+/// This AST node has three sub-expressions:
+///  - An OpaqueValueExpr with a source that is the argument lvalue expression.
+///  - An OpaqueValueExpr with a source that is an implicit conversion
+///    sequence from the source lvalue to the argument type.
+///  - An expression that assigns the second expression into the first,
+///    performing any necessary conversions.
+class HLSLOutArgExpr : public Expr {
+  friend class ASTStmtReader;
+
+  enum {
+    BaseLValue,
+    CastedTemporary,
+    WritebackCast,
+    NumSubExprs,
+  };
+
+  Stmt *SubExprs[NumSubExprs];
+  bool IsInOut;
+
+  HLSLOutArgExpr(QualType Ty, OpaqueValueExpr *B, OpaqueValueExpr *OpV,
+                 Expr *WB, bool IsInOut)
+      : Expr(HLSLOutArgExprClass, Ty, VK_LValue, OK_Ordinary),
+        IsInOut(IsInOut) {
+    SubExprs[BaseLValue] = B;
+    SubExprs[CastedTemporary] = OpV;
+    SubExprs[WritebackCast] = WB;
+    assert(!Ty->isDependentType() && "HLSLOutArgExpr given a dependent type!");
+  }
+
+  explicit HLSLOutArgExpr(EmptyShell Shell)
+      : Expr(HLSLOutArgExprClass, Shell) {}
+
+public:
+  static HLSLOutArgExpr *Create(const ASTContext &C, QualType Ty,
+                                OpaqueValueExpr *Base, OpaqueValueExpr *OpV,
+                                Expr *WB, bool IsInOut);
+  static HLSLOutArgExpr *CreateEmpty(const ASTContext &Ctx);
+
+  const OpaqueValueExpr *getOpaqueArgLValue() const {
+    return cast<OpaqueValueExpr>(SubExprs[BaseLValue]);
+  }
+  OpaqueValueExpr *getOpaqueArgLValue() {
+    return cast<OpaqueValueExpr>(SubExprs[BaseLValue]);
+  }
+
+  /// Return the l-value expression that was written as the argument
+  /// in source.  Everything else here is implicitly generated.
+  const Expr *getArgLValue() const {
+    return getOpaqueArgLValue()->getSourceExpr();
+  }
+  Expr *getArgLValue() { return getOpaqueArgLValue()->getSourceExpr(); }
+
+  const Expr *getWritebackCast() const {
+    return cast<Expr>(SubExprs[WritebackCast]);
+  }
+  Expr *getWritebackCast() { return cast<Expr>(SubExprs[WritebackCast]); }
+
+  const OpaqueValueExpr *getCastedTemporary() const {
+    return cast<OpaqueValueExpr>(SubExprs[CastedTemporary]);
+  }
+  OpaqueValueExpr *getCastedTemporary() {
+    return cast<OpaqueValueExpr>(SubExprs[CastedTemporary]);
+  }
+
+  /// returns true if the parameter is inout and false if the parameter is out.
+  bool isInOut() const { return IsInOut; }
+
+  SourceLocation getBeginLoc() const LLVM_READONLY {
+    return SubExprs[BaseLValue]->getBeginLoc();
+  }
+
+  SourceLocation getEndLoc() const LLVM_READONLY {
+    return SubExprs[BaseLValue]->getEndLoc();
+  }
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == HLSLOutArgExprClass;
+  }
+
+  // Iterators
+  child_range children() {
+    return child_range(&SubExprs[BaseLValue], &SubExprs[NumSubExprs]);
+  }
+};
+
 /// Frontend produces RecoveryExprs on semantic errors that prevent creating
 /// other well-formed expressions. E.g. when type-checking of a binary operator
 /// fails, we cannot produce a BinaryOperator expression. Instead, we can choose

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -4055,6 +4055,9 @@ DEF_TRAVERSE_STMT(OpenACCComputeConstruct,
 DEF_TRAVERSE_STMT(OpenACCLoopConstruct,
                   { TRY_TO(TraverseOpenACCAssociatedStmtConstruct(S)); })
 
+// Traverse HLSL: Out argument expression
+DEF_TRAVERSE_STMT(HLSLOutArgExpr, {})
+
 // FIXME: look at the following tricky-seeming exprs to see if we
 // need to recurse on anything.  These are ones that have methods
 // returning decls or qualtypes or nestednamespecifier -- though I'm

clang/include/clang/AST/TextNodeDumper.h

@@ -407,6 +407,7 @@ class TextNodeDumper
   void
   VisitLifetimeExtendedTemporaryDecl(const LifetimeExtendedTemporaryDecl *D);
   void VisitHLSLBufferDecl(const HLSLBufferDecl *D);
+  void VisitHLSLOutArgExpr(const HLSLOutArgExpr *E);
   void VisitOpenACCConstructStmt(const OpenACCConstructStmt *S);
   void VisitOpenACCLoopConstruct(const OpenACCLoopConstruct *S);
   void VisitEmbedExpr(const EmbedExpr *S);

clang/include/clang/Basic/Attr.td

@@ -4639,14 +4639,13 @@ def HLSLGroupSharedAddressSpace : TypeAttr {
   let Documentation = [HLSLGroupSharedAddressSpaceDocs];
 }
 
-def HLSLParamModifier : TypeAttr {
+def HLSLParamModifier : ParameterABIAttr {
   let Spellings = [CustomKeyword<"in">, CustomKeyword<"inout">, CustomKeyword<"out">];
   let Accessors = [Accessor<"isIn", [CustomKeyword<"in">]>,
                    Accessor<"isInOut", [CustomKeyword<"inout">]>,
                    Accessor<"isOut", [CustomKeyword<"out">]>,
                    Accessor<"isAnyOut", [CustomKeyword<"out">, CustomKeyword<"inout">]>,
                    Accessor<"isAnyIn", [CustomKeyword<"in">, CustomKeyword<"inout">]>];
-  let Subjects = SubjectList<[ParmVar]>;
   let Documentation = [HLSLParamQualifierDocs];
   let Args = [DefaultBoolArgument<"MergedSpelling", /*default*/0, /*fake*/1>];
 }

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12380,6 +12380,8 @@ def warn_hlsl_availability : Warning<
 def warn_hlsl_availability_unavailable :
   Warning<err_unavailable.Summary>,
   InGroup<HLSLAvailability>, DefaultError;
+def error_hlsl_inout_scalar_extension : Error<"illegal scalar extension cast on argument %0 to %select{|in}1out paramemter">;
+def error_hlsl_inout_lvalue : Error<"cannot bind non-lvalue argument %0 to %select{|in}1out paramemter">;
 
 def err_hlsl_export_not_on_function : Error<
   "export declaration can only be used on functions">;

clang/include/clang/Basic/Specifiers.h

@@ -385,6 +385,12 @@ namespace clang {
     /// Swift asynchronous context-pointer ABI treatment.  There can be at
     /// most one parameter on a given function that uses this treatment.
     SwiftAsyncContext,
+
+    // This parameter is a copy-out HLSL parameter.
+    HLSLOut,
+
+    // This parameter is a copy-in/copy-out HLSL parameter.
+    HLSLInOut,
   };
 
   /// Assigned inheritance model for a class in the MS C++ ABI. Must match order

clang/include/clang/Basic/StmtNodes.td

@@ -307,3 +307,6 @@ def OpenACCAssociatedStmtConstruct
     : StmtNode<OpenACCConstructStmt, /*abstract=*/1>;
 def OpenACCComputeConstruct : StmtNode<OpenACCAssociatedStmtConstruct>;
 def OpenACCLoopConstruct : StmtNode<OpenACCAssociatedStmtConstruct>;
+
+// HLSL Constructs.
+def HLSLOutArgExpr : StmtNode<Expr>;

clang/include/clang/Sema/SemaHLSL.h

@@ -71,6 +71,12 @@ class SemaHLSL : public SemaBase {
 
   // HLSL Type trait implementations
   bool IsScalarizedLayoutCompatible(QualType T1, QualType T2) const;
+
+  bool CheckCompatibleParameterABI(FunctionDecl *New, FunctionDecl *Old);
+
+  ExprResult ActOnOutParamExpr(ParmVarDecl *Param, Expr *Arg);
+
+  QualType getInoutParameterType(QualType Ty);
 };
 
 } // namespace clang